1. Field of the Invention
This invention relates to electrical switching apparatus and, more particularly, to circuit interrupters, such as, for example, aircraft or aerospace circuit breakers providing arc fault protection.
2. Background Information
Circuit breakers are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition. In small circuit breakers, commonly referred to as miniature circuit breakers, used for residential and light commercial applications, such protection is typically provided by a thermal-magnetic trip device. This trip device includes a bimetal, which heats and bends in response to a persistent overcurrent condition. The bimetal, in turn, unlatches a spring powered operating mechanism, which opens the separable contacts of the circuit breaker to interrupt current flow in the protected power system.
Subminiature circuit breakers are used, for example, in aircraft or aerospace electrical systems where they not only provide overcurrent protection but also serve as switches for turning equipment on and off. Such circuit breakers must be small to accommodate the high-density layout of circuit breaker panels, which make circuit breakers for numerous circuits accessible to a user. Aircraft electrical systems, for example, usually consist of hundreds of circuit breakers, each of which is used for a circuit protection function as well as a circuit disconnection function through a push-pull handle.
Typically, subminiature circuit breakers have provided protection against persistent overcurrents implemented by a latch triggered by a bimetal responsive to I2R heating resulting from the overcurrent. There is a growing interest in providing additional protection, and most importantly arc fault protection.
During sporadic arc fault conditions, the overload capability of the circuit breaker will not function since the root-mean-squared (RMS) value of the fault current is too small to actuate the automatic trip circuit. The addition of electronic arc fault sensing to a circuit breaker can add one of the elements required for sputtering arc fault protection—ideally, the output of an electronic arc fault sensing circuit directly trips and, thus, opens the circuit breaker. See, for example, U.S. Pat. Nos. 6,710,688; 6,542,056; 6,522,509; 6,522,228; 5,691,869; and 5,224,006.
Aircraft circuit breakers have employed various mechanisms to indicate fault events. For example, U.S. Pat. No. 6,542,056 discloses a movable and illuminable arc fault indicator having a ring portion and two leg portions internal to a housing. When energized by an arc fault current assembly in response to an arc fault trip condition, an arc fault actuator moves one of the leg portions internal to the housing, which, in turn, moves the ring portion external to the housing. The arc fault current assembly includes a light emitting diode for illuminating the ring portion through the other one of the leg portions when the arc fault current assembly is properly powered and in the absence of an arc fault trip condition.
It has become more and more difficult to incorporate the illuminable ring portion for arc fault indication, since the physical size of aircraft circuit breakers has decreased.
It is known to provide an aircraft circuit breaker including a behind-the-panel indicator to indicate to maintenance personnel the functionality of the circuit breaker electronic components. Hence, the aircraft panel must be opened, with power on, in order to inspect the behind-the-panel indicator. This takes time/cost to inspect, cannot be performed during pre-flight check by the pilot and exposes the maintenance personnel to hazardous voltages.
Accordingly, there is room for improvement in panel-mounted electrical switching apparatus and circuit breakers, which indicate status.